The “background” description provided herein is for the purpose of generally presenting the context of the invention. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Integrated circuits (ICs) are increasingly modular in construction. To this end, ICs are often configured to operate using multiple voltage domains. The different voltages may be used to power cell/blocks of the IC and may also be provided to I/O pads of the IC. For stacked I/O pads, the use of different voltage domains is typically geared toward supporting one or more I/O voltage levels. For example, an IC may operate at either 1.8V or 3.3V.
This type of pad usually requires 3.3V devices to implement the pad logic. Output drivers also need to operate at 3.3V without voltage stress. However, it is also possible to implement the pad logics and output drivers using 1.8V devices. The 1.8V devices are stacked for the output drivers to relieve the full 3.3V output voltage swing during operation. This stacked implementation saves the cost of an extra mask that would otherwise be needed to fabricate the 3.3V devices. This type of pad requires information relating to the I/O voltage level to configure the pad to a correct voltage level. Otherwise the pad will not function correctly and/or the devices may be stressed, which may cause long term reliability problems.